Method for producing an aqueous hydroxylamine solution devoid of salt

ABSTRACT

The invention relates to a method for producing a highly pure, aqueous hydroxylamine solution by distilling an aqueous solution, devoid of salt, of a hydroxyl ammonium salt in a plate column comprising at least two mechanical plates. Said method is characterised in that packing bodies are arranged between at least two plates of the plate column over the cross-section of said column.

[0001] The present invention relates to a process for the preparation ofa highly pure, aqueous hydroxylamine solution by distillation of asalt-free, aqueous hydroxylamine solution in a plate-type column havingat least two mechanical plates, wherein, between at least two plates ofthe plate-type columns, packing materials are situated over the crosssection of the column.

[0002] Highly pure, concentrated, aqueous hydroxylamine solutions areused, inter alia, in the electronics industry, e.g. in combination withother substances for cleaning platens or silicon wafers. For use in theelectronics industry, concentrations of the impurities, in particularmetal ions, of far less than 1 ppm, “electronic grade” ware, arecustomarily required. At the same time, the demands on the purity of theaqueous hydroxylamine solutions are continuously increasing.

[0003] Highly pure, concentrated, aqueous hydroxylamine solutions arecustomarily prepared from salt-free, aqueous hydroxylamine solutions.

[0004] Hydroxylamine is prepared on a large scale as a hydroxylammoniumsalt, customarily as hydroxylammonium sulfate. For the preparation ofsalt-free, aqueous hydroxylamine solutions, an aqueous solution of ahydroxylammonium salt is treated with a base and an aqueoushydroxylamine solution is separated from the mixture, customarily bydistillation, for example according to U.S. Pat. No. 5,472,679, WO97/22551, WO 98/57886, WO 97/22550, WO 99/07637. Dilute, salt-free,aqueous hydroxylamine solutions are customarily obtained here.

[0005] Highly pure, concentrated, aqueous hydroxylamine solutions arecustomarily obtained from such dilute, salt-free, aqueous hydroxylaminesolutions by distillation again, for example according to U.S. Pat. No.5,472,679, WO 97/22551, WO 98/57886, WO 97/22550, WO 99/07637.

[0006] EP 188 387 A2 discloses a packed fractionation column having,above and below the feed lines and take-off locations, mechanical trayscharacterized by their higher pressure drop and the higher liquidhold-up thereby ameliorating any fluctuations which may otherwise act onthe packing due to supply or removal of column contents. This column isrecommended in particular when the stream to be fractionated passes intothe column in a supercooled or superheated state. K. Sattler (ed.):Thermische Trennverfahren, 3rd edition, Wiley-VCH, Weinheim 2001, p.242-249, gives an overview of various packings and packing elementscolumns. D. W. Green (ed.): Perry's Chemical Engineer's Handbook,McGraw-Hill, New York 1997, p. 14-21 to 14-61 gives an overview ofgas-liquid contact apparatus such as, for example, column trays or traycolumns and also structured packings, dumped packings and columns packedwith structured packings and dumped packings.

[0007] U.S. Pat. No. 6,235,162 discloses a two-stage process forpurifying hydroxylamine solutions which involves a first stage in whichvolatile constituents (such as organic solvents, ammonia, nitrogen orother gases) are expelled from the solution via a packed column. Asubsequent second stage comprises the hydroxylamine solution which hasremained in the receiving flask and has been freed of volatileconstituents being subjected to a flashover distillation to free it ofnonvolatile constituents.

[0008] The distillation of aqueous, hydroxylamine-containing solutions,even on the laboratory scale, is indicated as being a particularlyhazardous operation: see Roth-Weller: Gefährliche Chemische Reaktionen,Stoffinformationen Hydroxylamin (Hazardous Chemical Reactions, SubstanceInformation for Hydroxylamine), page 3, 1984, 2, Eco-med-Verlag.

[0009] Accordingly, the distillation mentioned demands high technicalexpenditure and a large time requirement.

[0010] Moreover, highly pure, concentrated, aqueous hydroxylamine.solutions, despite the second distillation, contain impurities frompreparation, such as sodium sulfate or other metal compounds, inundesirably large amounts.

[0011] The present invention was therefore based on the object of makingavailable a process for the preparation of highly pure, concentrated,aqueous hydroxylamine solutions by distillation, in which the highlypure, concentrated, aqueous hydroxylamine solutions are obtained withfewer impurities without increasing the technical expenditure, the timerequirement or a safety risk.

[0012] Highly pure within the meaning of the present invention isunderstood as meaning metal ion contents of less than 1 ppm andhydroxylamine contents of more than 20% by weight of hydroxylamine basedon the solution.

[0013] Accordingly, the process defined at the outset has been found.

[0014] In the process according to the invention, a salt-free, aqueoushydroxylamine solution is employed. The preparation of such solutions isknown per se and can be carried out, for example, by the processes as inU.S. Pat. No. 5,472,679, WO 97/22551, WO 98/57886, DE 1954775.8 or WO99/07637.

[0015] Such salt-free, aqueous hydroxylamine solutions in general have acontent of hydroxylamine of 10 to 300, preferably 80 to 150, g/liter anda content of impurities, such as sodium sulfate or metal ions, in therange from 0.005 to 25 ppm.

[0016] According to the invention, a salt-free, aqueous hydroxylaminesolution is distilled in a plate-type column having at least 10practical plates.

[0017] Suitable plates are cross flow plates such as perforated plates,valve plates, bubble plates and tunnel plates or dual flow plates,preferably perforated plates. The distances of the plates from oneanother should be in the range from 200 to 900 mm, preferably 300 to 600mm.

[0018] The column and plates can be manufactured from nonmetallicmaterials, such as glass, ceramic, plastics. By this means thedecomposition initiated by metal ions is excluded. Surprisingly, it hasbeen shown, however, that the column can also be manufactured fromspecial metallic materials, such as platinum, silver or zirconium,without a significantly increased decomposition of the hydroxylaminebeing observed.

[0019] Advantageously, a falling film evaporator is used for heating thebottom of the column; of course, other customary bottom heaters, such asnatural or forced recirculation evaporators, plate heat exchangers etc.can also be employed.

[0020] The reflux ratio in the concentrator part can advantageously beadjusted such that it is in the range from 0.2 to 2.

[0021] According to the invention, above at least one plate of theplate-type column over the cross section of the column are situatedclassical packing materials such as Raschig rings, Pall rings, saddlebodies, modern high-efficiency packing materials such as the Hiflow ring(Rauschert (Steinwiesen, Germany)), super Raschig rings (Raschig(Ludwigshafen, Germany)), cascade mini-rings (Koch-Glitsch (Wichita,USA)), IMTP rings (Norton (Akron, USA)) or Nutter rings (Sulzer Chemtech(Wintherthur, Switzerland)) or structured packings such as Mellapak,Mellapak Plus or textile packing, preferably modern high-efficiencypacking materials.

[0022] The packing materials should be inert to the solution to bedistilled, for example made of plastics or special metallic materials,preferably of perfluorinated plastics (e.g. TFM, PFA, Teflon).

[0023] The packing height of the packing materials between the platesshould be 50 to 300 mm, preferably 100 mm to 200 mm. The distancebetween the packing material charge and the plate above which thepacking material charge is installed is between 0 and 600 mm, preferably100 mm to 300 mm. The distance between the packing material charge andthe plate below which the packing material charge is installed is 0 to300 mm, preferably 30 to 100 mm.

[0024] Before the use of the process according to the invention, it maybe advantageous to add a stabilizer. Suitable stabilizers are known perse and commercially obtainable.

[0025] The hydroxylamine solution can advantageously be fed in at aheight of approximately one third of the theoretical plate number of theplate-type column. Over the head largely hydroxylamine-free water isobtained and at the bottom a hydroxylamine solution whose concentrationis dependent on the distillation conditions.

[0026] In general, the distillation column is operated using a pressurein the range from 1 to 200 kPa (0.01 to 2 bar), preferably 5 to 120 kPa(0.05 to 1.2 bar), particularly preferably 30 to 110 kPa (0.3 to 1.1bar), the pressure in each case relating to the pressure at thehead/bottom of the column. The more highly the hydroxylamine is to beconcentrated, the more gently (lower pressure and low temperature) itmust be distilled. The distillation can be carried out continuously orbatchwise.

[0027] The temperatures prevailing in the distillation column depend onthe pressure at which the distillation column is operated. They are ingeneral in the range from 10 to 160° C., preferably 60 to 110° C.

[0028] The water or the vapor removed over the head of the distillationcolumn can be fed back again directly or after compression orsuperheating as strip steam into the bottom of the column employed inthe process according to the invention or fed to waste water processingas waste water.

[0029] If appropriate, a device for the separation of droplets which arecarried over, for example a demister, can be installed above the feedplate.

[0030] The concentrated, aqueous hydroxylamine solution, whichpreferably has a hydroxylamine content of more than 20, preferably morethan 40 and in particular more than 50, % by weight of hydroxylamine andless than 1 ppm, in particular less than 0.1 ppm, of metal ions (inparticular from the preparation or the materials used for thepreparation and recovery), is in general obtained as the bottom product.

[0031] The highly pure, aqueous hydroxylamine solution obtained by theprocess according to the invention has a higher purity than a solutionobtained by known distillation processes. In addition, the loss ofhydroxylamine by means of the water to be purged is lower. Moreover, theresidence time of the distillation mixture in the column is shorter andthus the thermal stress is lower than in known processes. Further, thecapacity of the column is increased with the same column size and thesame holdup of the column. If the column contains a demister, the burdenon this is relieved compared with a known process.

EXAMPLES Comparative Example 1

[0032] In a plate-type column having 33 plates and a diameter of 1.3 m,a solution of 8.9% by weight hydroxylamine (free base) in water wasadded to the 8 plates from below in an amount of 2.2 t/h.

[0033] At the head, an amount of 1.9 t/h of water having a hydroxylaminecontent of 1500 ppm by weight was removed at a reflux rate of 0.9 t/hand an addition of 10 kg/h of stabilizer.

[0034] At the bottom, 350 kg/h of a solution of 50% by weighthydroxylamine in water were removed.

[0035] The pressure loss over the column was 100 mbar, the energy inputinto the bottom evaporator 2.8 t/h of steam.

Example 1

[0036] The procedure was as in comparison example 1 with the exceptionthat in each case a 150 mm high charge of Hiflow rings 38/1 (Rauschert,Steinwiesen, Germany) was situated on the plates.

[0037] The results as in comparative example 1 were obtained, with theexception that the water obtained as a head product only contained 1000ppm by weight of hydroxylamine.

Example 2

[0038] The procedure was as in example 1 with the exception that thefeed was 3.4 t/h.

[0039] At the head, an amount of 2.9 t/h of water having a hydroxylaminecontent of 1000 ppm by weight was removed at a reflux rate of 1.4 t/hand an addition of 15 kg/h of stabilizer.

[0040] At the bottom, 540 kg/h of a solution of 50% by weighthydroxylamine in water were removed.

[0041] The pressure loss over the column was 130 mbar, the energy inputinto the bottom evaporator 4.3 t/h of steam.

We claim:
 1. A process for the preparation of a highly pure, aqueoushydroxylamine solution by distillation of a salt-free, aqueoushydroxylamine solution in a plate-type column having at least twomechanical plates, wherein, above at least one plate of the plate-typecolumn, packing materials are situated over the cross section of thecolumn.
 2. A process as claimed in claim 1, the plate-type column having10 to 50 mechanical plates.
 3. A process as claimed in claim 1 or 2, thepacking materials employed being classical packing materials,high-efficiency packing materials or structured packings.
 4. A processas claimed in claims 1 to 3, the temperature in the plate-type columnbeing in the range from 10° C. to 160° C.
 5. A process as claimed inclaims 1 to 4, the plate-type columns employed being a cross flowplate-type column or dual flow plate-type column.